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Re: thoughts from Tuesday telecon

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 23 Sep 2005 10:34:19 -0400 (EDT)
Message-Id: <20050923.103419.107966309.pfps@research.bell-labs.com>
To: phayes@ihmc.us
Cc: public-rdf-dawg@w3.org, connolly@w3.org, horrocks@cs.man.ac.uk, franconi@inf.unibz.it, bparsia@isr.umd.edu

Your notes have an example where a SPARQL query includes a bnode.    

The use of blank nodes in a SPARQL query is given two opposing meanings:

Meaning 1:

	2.4 Pattern Solutions

	Definition: Pattern Solution

	A pattern solution is a substitution function from a subset of the set
	of variables to the set of RDF terms, RDF-T. 

	The result of replacing every v in a graph pattern P by S(v) is written S(P).

	If variable v is not in the domain of S then S(v) is defined to be v.

	Definition: Query Solution

	Given query Q = (GP, DS, SM, R) then S is a query solution of Q if S is
	a pattern solution for GP matching dataset DS. 

Meaning 2:

	2.7 Blank Nodes

	Blank Nodes and Queries

	A blank node can appear in a query pattern. It behaves as a variable; a blank
	node in a query pattern may match any RDF term. 

Your use of blank nodes in a query corresponds to the first meaning, which, as
it is the formal definition of solutions, I take to be authoritative.  However,
as there is a second meaning, it would be better to be very explicit as to
which meaning you are using.

Peter F. Patel-Schneider
Received on Friday, 23 September 2005 14:37:14 UTC

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